I'm studying for an actuarial exam and it always confuses me when I'm trying to count intervals in annuities.
For example, if I want to know how many payment periods there are from period 13 to period 27, what is the length of this interval?
A more general example of my problem would be to count the numbers between 99 and 56.
What are some general tips when doing this sort of counting? P.S. sorry I don't know the proper tags for this question.